---
title: Querying Data 
---

This topic provides information about using SQL in Greenplum databases.

You enter SQL statements called queries to view, change, and analyze data in a database using the `psql` interactive SQL client and other client tools.

-   **[About Greenplum Query Processing](../../query/topics/parallel-proc.html)**  
This topic provides an overview of how Greenplum Database processes queries. Understanding this process can be useful when writing and tuning queries.
-   **[About GPORCA](../../query/topics/query-piv-optimizer.html)**  
In Greenplum Database, the default GPORCA optimizer co-exists with the Postgres Planner.
-   **[Defining Queries](../../query/topics/defining-queries.html)**  
Greenplum Database is based on the PostgreSQL implementation of the SQL standard.
-   **[WITH Queries \(Common Table Expressions\)](../../query/topics/CTE-query.html)**  
The `WITH` clause provides a way to use subqueries or perform a data modifying operation in a larger `SELECT` query. You can also use the `WITH` clause in an `INSERT`, `UPDATE`, or `DELETE` command.
-   **[Using Functions and Operators](../../query/topics/functions-operators.html)**  
Description of user-defined and built-in functions and operators in Greenplum Database.
-   **[Working with JSON Data](../../query/topics/json-data.html)**  
Greenplum Database supports the `json` and `jsonb` data types that store JSON \(JavaScript Object Notation\) data.
-   **[Working with XML Data](../../query/topics/xml-data.html)**  
Greenplum Database supports the `xml` data type that stores XML data.
-   **[Using Full Text Search](../../textsearch/full-text-search.html)**  
Greenplum Database provides data types, functions, operators, index types, and configurations for querying natural language documents.
-   **[Using Greenplum MapReduce](../../query/topics/gp-mapreduce.html)**  
MapReduce is a programming model developed by Google for processing and generating large data sets on an array of commodity servers. Greenplum MapReduce allows programmers who are familiar with the MapReduce model to write map and reduce functions and submit them to the Greenplum Database parallel engine for processing.
-   **[Query Performance](../../query/topics/query-performance.html)**  
Greenplum Database dynamically eliminates irrelevant partitions in a table and optimally allocates memory for different operators in a query.
-   **[Managing Spill Files Generated by Queries](../../query/topics/spill-files.html)**  
Greenplum Database creates spill files, also known as workfiles, on disk if it does not have sufficient memory to run an SQL query in memory.
-   **[Query Profiling](../../query/topics/query-profiling.html)**  
Examine the query plans of poorly performing queries to identify possible performance tuning opportunities.

**Parent topic:** [Greenplum Database Administrator Guide](../../admin_guide.html)

